Justin Timberlake's evolution from teenaged *NSYNC heart-throb to grown-up pop titan blazed a trail for other one-time idols. Justin Bieber's transition from puppy-eyed love songs to EDM brooding, Nathan Sykes' maturation from cheeky member of The Wanted to serious soul man, and Nick and Joe Jonas' post-Jonas Brothers explorations of wounded soul and uptempo party funk all follow the path JT took during his post-boy-band years.